This invention relates generally to medical devices, and more particularly concerns an improved ultrasound transmission member for use in an ultrasonic catheter for treatment of blockages of hollow anatomical structures.
In typical percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter having a preformed distal tip is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and is advanced therein until the distal tip thereof is in the ostium of the desired coronary artery. A guide wire and a dilatation catheter having a balloon on the distal end thereof are introduced through the guiding catheter with the guide wire slidably disposed within an inner lumen of the dilatation catheter. The guide wire is first advanced into the patient""s coronary vasculature until the distal end thereof crosses the lesion to be dilated and then the dilatation catheter is advanced over the previously introduced guide wire until the dilatation balloon is properly positioned across the lesion. The balloon may then be inflated to treat the lesion. Thereafter, a stent device may be located at the treated lesion, if deemed necessary.
In xe2x80x9cultrasonicxe2x80x9d angioplasty, an ultrasonic angioplasty catheter is similarly advanced to an area of vascular blockage, and mechanical vibration at ultrasonic frequencies, generated typically by a piezoceramic transducer, is delivered along an ultrasonic angioplasty transmission member or wire to a distal catheter tip. When the distal catheter tip is abutted against intravascular blockage, the vibration of the distal end of the ultrasonic angioplasty transmission member removes the obstruction by mechanical impact and cavitation. However, such ultrasonic angioplasty transmission members frequently suffer from high-cycle fatigue, which can result in fracturing or breakage of the members during use.
Ultrasonic angioplasty transmission members are commonly connected to an extra-corporeal source of ultrasonic energy, so that it is generally necessary to deliver the ultrasonic energy over a relatively long distance, such as approximately 150 cm, to the intravascular blockage to be treated. Over such a distance, the ultrasonic energy attenuates as it passes along the length of the ultrasonic angioplasty transmission member resulting in a loss of system efficiency. To compensate for the loss, a greater amount of acoustical energy is delivered to the ultrasonic angioplasty transmission member at its proximal end than what actually reaches the treatment site. This delivery of higher levels of acoustic energy can increase fatigue and the chances of fracturing and breakage of the ultrasonic angioplasty transmission member during use. It is therefore desirable to provide an ultrasonic angioplasty transmission member that has a lower loss of the ultrasonic energy transmitted by the member so that lower levels of energy may be applied to the member.
In ultrasonic angioplasty techniques, accurate positioning of the ultrasound transmission member in the vasculature system to be treated requires a highly flexible ultrasonic delivery system with a low profile, especially for coronary ultrasonic angioplasty procedures, so that the catheter can more easily navigate the various vascular passages to be advanced to the occlusion. Nickel-titanium superelastic alloys have been useful in these respects as an ultrasound transmission member. Tapering or narrowing the distal end of an ultrasound transmission member to enhance flexibility of the ultrasound transmission member at its distal end is known from U.S. Pat. No. 5,304,115 (Pflueger et al.). While such tapering or narrowing typically decreases the rigidity and improves the bendability of the ultrasound transmission member, a significant increase in amplitude of the ultrasonic energy occurs at the tapered or narrowed region. Such an increase in amplitude can cause an increased likelihood of fracturing or breakage of the ultrasound transmission member at that point during use.
While it is known to harden ultrasonic angioplasty transmission members to reduce fracturing or breakage, as disclosed in U.S. Pat. No. 5,304,115 (Pflueger et al.), by providing a hard coating or skin, it would be desirable to constrain transverse vibration at narrowed or tapered areas of an ultrasonic angioplasty transmission member to reduce stress and to lessen the chances of fracturing at such areas where amplification of ultrasonic energy can occur, while still allowing longitudinal movement. Additionally, it has been found that providing a hard coating or skin to reduce stress and attempt to prevent fracturing can contribute to attenuation of vibration of the ultrasonic angioplasty transmission member and inhibit longitudinal movement.
Hence those skilled in the art have recognized a need for an ultrasound transmission member providing improved characteristics of strength, fatigue resistance, elasticity, and energy transmission for an ultrasonic delivery system for use in the treatment of intravascular blockages. It is also desirable that measures to reduce fracturing or breakage of such ultrasonic angioplasty transmission members not interfere with properties such as sonic propagation, tensile strength, and flexibility to navigate sharp bends and curves in the vasculature. The present invention fulfills these needs and others.
Briefly, and in general terms, the present invention is directed to an improved ultrasound transmission member for use in an ultrasonic angioplasty device, the ultrasound transmission member having a proximal end configured to be connected to an ultrasound transducer and a distal end for applying ultrasonic energy to an area of vascular blockage, and the ultrasound transmission member having a distal portion with at least one amplification region of reduced cross-sectional diameter where transverse vibration of ultrasonic energy transmitted by the ultrasound transmission member is amplified, the ultrasound transmission member comprising a constraining member disposed around the amplification region to reduce transverse vibration at the amplification region, to thereby lower stress and reduce fractures of the ultrasound transmission member while allowing longitudinal movement of the ultrasound transmission member.
In another aspect, the invention is directed to an ultrasonic angioplasty catheter device comprising an elongate flexible catheter having a proximal end, a distal end, and at least one lumen extending longitudinally therethrough, the catheter device comprising an ultrasound transmission member extending through aid lumen and having a distal end with a head for applying ultrasonic energy to an occlusive lesion, and a proximal end configured to be connected to an ultrasound generating device, the ultrasound transmission member having a distal portion with at least one amplification region of reduced cross-sectional diameter where transverse vibration of ultrasonic energy transmitted by the ultrasound transmission member is amplified wherein the ultrasound transmission member comprises a constraining member disposed around the amplification region to reduce transverse vibration at the amplification region to thereby lower stress and reduce fractures of the ultrasound transmission member while allowing longitudinal movement of the ultrasound transmission member.
In more detailed aspects, the ultrasound transmission member comprises a first generally cylindrical section of the ultrasound transmission member having a first cross-sectional diameter, and a second generally cylindrical section of the ultrasound transmission member distal to the first section and having a second cross-sectional diameter that is smaller than the first cross-sectional diameter, the amplification region being formed at a proximal portion of the second generally cylindrical section. The ultrasound transmission member further comprises a plurality of generally cylindrical sections, each of the plurality of generally cylindrical sections having reduced cross-sectional diameter relative to a proximal adjacent section resulting in a plurality of amplification regions in the cylindrical sections of reduced cross-sectional diameter, wherein the constraining member is disposed around at least one of the amplification regions of the reduced diameter cylindrical sections to reduce transverse vibration at the amplification regions. The ultrasound transmission member further comprises a conically tapered section interposed between the first and second cylindrical sections.
In further aspects, the ultrasound transmission member further comprises a plurality of conically tapered sections interposed between adjacent ones of the plurality of generally cylindrical sections. Additionally, the ultrasound transmission member comprises an end cylindrical section, a penultimate cylindrical section immediately adjacent and proximal to the end cylindrical section, and a cylindrical section immediately adjacent and proximal to the penultimate cylindrical section having a larger diameter than the penultimate cylindrical section, the end cylindrical section having a cross-sectional diameter that is larger than the penultimate cylindrical section, and the constraining member being disposed over the end cylindrical section and over the penultimate cylindrical section and over the larger diameter cylindrical section immediately adjacent and proximal to the penultimate cylindrical section.
In yet further detail, the ultrasound transmission member comprises an end cylindrical section, a penultimate cylindrical section immediately adjacent and proximal to the end cylindrical section, the end cylindrical section having a cross-sectional diameter that is larger than the penultimate cylindrical section, a larger cylindrical section immediately adjacent and proximal to the penultimate cylindrical section having a larger diameter than the penultimate cylindrical section, and a conically tapered section immediately adjacent and proximal to the larger cylindrical section, and the constraining member being disposed over the end cylindrical section and over the penultimate cylindrical section and over the larger diameter cylindrical section immediately adjacent and proximal to the penultimate cylindrical section and over the conically tapered section immediately adjacent and proximal to the larger diameter cylindrical section.
In more detailed aspects, the constraining member is formed of a non-metallic material, such as shrink tubing, rubber, or plastic.
In other detailed aspects, the ultrasonic transmission member is in a fixed position within the catheter lumen and is connected to a distal head positioned on the distal end of said ultrasound member such that the distal head extends beyond the distal end of the catheter. The distal head comprises a larger diameter distal portion positioned beyond the distal end of the catheter and a smaller diameter portion located between the distal portion and the ultrasound transmission member and extending within the catheter. The ultrasound transmission member is formed at least partially of a superelastic metal alloy. In another aspect, the ultrasound transmission member is formed at least partially of a shape memory alloy that exhibits superelastic properties when in its martensitic state, and in yet a further aspect, the ultrasound transmission member is formed of a nickel-titanium alloy.
In yet further aspects, the distal head comprises a guide wire aperture to permit passage of a guide wire therethrough. Also, the region of reduced cross-sectional diameter is located within 5 cm to 30 cm of the distal end of the ultrasound transmission member. The ultrasound transmission member has a smaller diameter towards its distal end and increases to a larger diameter towards its proximal end.
In further aspects in accordance with the invention, there is provided an ultrasound transmission member for use in an ultrasonic angioplasty device, the ultrasound transmission member having a proximal end configured to be connected to an ultrasound transducer and a distal end for applying ultrasonic energy to an area of vascular blockage, the ultrasound transmission member comprising an elongated shaft including, in atomic percent, from about 28 to about 52 percent nickel, from about 48 to about 52 percent titanium, and up to about 20 percent of at least one alloying element selected from the group consisting of palladium, chromium, and hafnium. In further detail, the alloying element is hafnium or palladium, and is present, in atomic percent, in a range from about 3 to about 20 percent.
In further aspects, the alloying element is present, in atomic percent, in a range from about 5 to about 11 percent. The alloying element is palladium. In another aspect, the alloying element is chromium and is present, in atomic percent, in a range up to about 3 percent.
In yet a further aspect, the alloying element is present, in atomic percent, in a range from about 0.1 to about 1.0 percent. In another detailed aspect, the alloying element is present, in atomic percent, in a range from about 0.2 to about 0.5 percent.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example, the features of the invention.